Apparently the one combo box that intially gets the focus kept changing when the user scrolled the mouse wheel. This even happened after the user clicked on the vertical scrollbar.
The reaction from most people on the project was to say thats how the control with the focus behaves. However I take all trouble tickets seriously and did not want to blow off the concern. So I consulted what Microsoft Word does in this scenario. And sure enough - Word will not scroll the control in focus if you click on the scrollbar and scroll the mouse wheel. Microsoft Word scrolls the whole dialog screen.
So far I have only started looking at ways to quickly fix this problem. At first I hacked in a handler for WM_LBUTTONDOWN on the main dialog. The handler tried to to send a WM_KILLFOCUS to the control that had focus. Like most hacks this did not work. And what did I do? Make a more complex hack. I created separate hidden button to which I switched the focus on WM_LBUTTONDOWN.
The hacks only worked for some left mouse clicks on the dialog. If you click on the scroll bar area, you need to handle WM_NCLBUTTONDOWN because that is a non-client area of the dialog. This hackology was getting too deep without consistent results. So now its time to go back to the drawing board to fix this problem right. Any ideas?